Field of the Invention
This invention relates generally to polyethylene oxide copolymers that contain fluorinated groups, and, more specifically, to electrolytes that employ such polymers.
Poly(ethylene oxide) (PEO) is a well-known polymer electrolyte for lithium ion batteries due to its ability to dissolve lithium salts and its relatively high ionic conductivity at elevated temperatures. However, ionic conductivity of PEO at room temperature is about 10−5 S/cm, which is below ionic conductivities (greater than 10−3 S/cm) that are desirable for commercial applications. Low PEO ionic conductivity may be due to its crystalline nature at room temperature, as above 55° C., the melting temperature (Tm) of PEO, the ionic conductivity reach values of 10−4 S/cm or more.
Polymers made from perfluoro functional groups, such as perfluoro alkanes (PFA), are low Tg (less than −100° C.), non-flammable and chemically inert polymers, which might make them useful as electrolytes in electrochemical cells. But, unfortunately they also have low dielectric constants (DCs) and poor salt dissolution ability, which works against their suitability as electrolytes for electrochemical cells.
It would be useful to find a way to combine PEO and PFA polymers to make electrolytes that exploit the useful properties of both.